BootCamp Install button is greyed out

Can you please create USB Installer first? If it is still greyed out, please run the following two procedures

Resetting the System Management Controller (SMC) on your Mac - Apple Support

How to Reset NVRAM on your Mac - Apple Support

and test?

You still have a possibility that the MBR corresponding to the Windows side has not been cleaned yet.

Please post the output of the following OSX Terminal commands.

diskutil list

diskutil cs list

sudo gpt -vv -r show /dev/disk0

sudo fdisk /dev/disk0

The "sudo" commands will prompt for your password, and it will not be echoed back. You may also see a warning about improper use of "sudo" and potential data loss due to "abuse" of the command.

There is a large chunk of free space after GPT3. It should be converted to a FAT32 partition and a new MBR created to allow BC Assistant's Install option to be used. What year is your Macbook Pro?

Windows can be installed by using two methods on Macs after Late 2013. The traditional method is using BIOS emulation and a MBR. This is the legacy (older) method. Later models support UEFI/EFI Boot. The current Free Space chunk can be used as it is now to install W8 or W10 using this method. W7 has some challenges with EFI booting and driver issues like GPU and audio.

The EFI method is faster because it eliminates BIOS emulation.

Windows cannot be installed on USB/Firewire disks, but it can be installed on Thunderbolt/PCI/SATA storage.

You can install it in the Free Space after GPT3. It will be split into MSR (System Reserved) and MSD (Data) partitions by the EFI installer.

40 Free Go confused me first, but I assume you mean the Free Space of 40gigabytes after Recovery HD. 😉

The steps are the same for W8. I would recommend W8.1. Burn your ISO installer to a USB. Power down your Mac, poor it up and use Alt/Option and choose the USB installer. When prompted for the destination partition, point it to the Free Space part.

I have the EFI setup on my son's Late 2013 15-in rMBP. Here is the disk layout. GPT4 is MSR and GPT5 is MS Data.

gpt show: /dev/disk0: mediasize=500277790720; sectorsize=512; blocks=977105060

gpt show: /dev/disk0: PMBR at sector 0

gpt show: /dev/disk0: Pri GPT at sector 1

gpt show: /dev/disk0: Sec GPT at sector 977105059

start size index contents

0 1 PMBR

1 1 Pri GPT header

2 32 Pri GPT table

34 6

40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B

409640 487712920 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC

488122560 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC

489392096 32

489392128 262144 4 GPT part - E3C9E316-0B5C-4DB8-817D-F92DF00215AE

489654272 487450624 5 GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7

977104896 131

977105027 32 Sec GPT table

977105059 1 Sec GPT header

sudo fdisk /dev/disk0

Disk: /dev/disk0 geometry: 60821/255/63 [977105060 sectors]

Signature: 0xAA55

Starting Ending

#: id cyl hd sec - cyl hd sec [ start - size]

------------------------------------------------------------------------

1: EE 1023 254 63 - 1023 254 63 [ 1 - 977105059] <Unknown ID>

2: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

3: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

4: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

Do you have a choice of Windows and EFI Boot? If yes, choose EFI Boot.